1. Field of the Invention
The present invention relates to a carrier system for carrying a cargo in the vicinity of a ceiling to transfer the cargo to a rack or the like, and a method for controlling the same.
2. Description of the Related Art
There has hitherto been known a carrier system for making a carrier travel along a rail hung on a ceiling to carry a cargo in the vicinity of the ceiling. The carrier used for this carrier system includes a travelling vehicle that travels along the rail, and a lift stage liftably hung on the travelling vehicle by means of a hanging member having flexibility. For example, when storing cargo in a rack arranged along the rail, the carrier moves along the rail to a position of the rack, and the lift stage is lowered to a height of a placement part for storing the cargo in the rack, and thereafter, the cargo is stored on the placement part.
In a carrier system described in Unexamined Japanese Patent Publication No. 63-242809, a plurality of carriers are made to travel along a circulation rail so as to rapidly carry a large number of cargoes.
However, in the carrier system described in Unexamined Japanese Patent Publication No. 63-242809, since the carrier stops while being hung on the circulation rail while a cargo is transferred between the carrier and a rack, travelling of another carrier that travels along the rail may be disturbed. Hence rapid carriage of a cargo by the other carrier may be prevented.